This invention relates to chucks for holding a workpiece in a machine such as a lathe.
A variety of chucks or gripping devices are known in the machine and tool industry for holding a workpiece or a tool bit. Many of these chucks have movable or sliding jaws which can be moved radially inwardly or outwardly in order to hold or grip the end of a workpiece or a tool bit. These jaws are sometimes moved by means of a special tool or key that is turned manually.
One common form of chuck used with a lathe is called a scroll chuck which can be of the self-centering type. Although the number of jaws in chucks of this type can vary, in many cases these chucks are equipped with three or four jaws that can be moved radially inwardly or outwardly by means of an annular scroll member that is turned about a central axis in order to manoeuvre the jaws. Scroll chucks have several advantages including versatility and ease of use. One form of improved scroll chuck is that disclosed in and illustrated in applicant's own U.S. Pat. No. 5,141,239 which issued Aug. 25, 1992, the disclosure of which is incorporated herein by reference. With this improved scroll chuck the possibility of one or more of the jaws of the chuck becoming accidentally disengaged is substantially reduced.
U.S. Pat. No. 4,630,836 issued Dec. 23, 1986 to Hilti Aktiengesellschaft describes a chuck suitable for use in a drill such as a hammer drill, which chuck has clamping jaws to secure a tool. These jaws each have a convex surface transverse to the chuck axis. The more radially inward portion of the convex surface has a V-shaped notch extending in the axial direction of the chuck and this notch forms a pair of spaced edges which are said to grip the surface of the tool so that it can be reliably rotated. In the illustrated version of this chuck, there are three clamping jaws.
It is an object of the present invention to provide an improved chuck for holding a workpiece in the machine wherein the jaw devices are provided with an unique improved profile that provides better gripping or holding power, whether the workpiece be round or square in cross-section.
It is a further object of the present invention to provide a chuck for holding a workpiece which has improved jaw devices that can be readily manufactured without undue difficulty and that are easy to use when working with a machine such as a lathe.